1. Field of Invention The present invention relates to an insulating enamel and more particularly to a surge-resistant insulating enamel with excellent abrasion resistance and flexibility for application to a conductor to form an enameled wire.
2. Description of the Related Art
Recent environmental events have encouraged many countries to save energy and reduce CO2 emission. Therefore, several protocols and strategies have been established, including energy-saving inverters. Inverters control the rotation speed of the motor by changing voltage and frequency. Therefore, the motor has improved loading and drive efficiencies. Accordingly, regenerative power can be used for a motor with the inverter because the inverter saves energy.
Inverters can also be applied to various other systems, including intelligent power modules (IPMs) using the inverter due to its small size and reduced cost. Furthermore, multiple inverters may be connected to each other to form an inverter network for building remote control and maintenance system or the like.
Power stations transmit electricity with normal voltage (110 volt). A surge occurs when transient voltage is higher than the normal voltage. The surge can be observed in an oscilloscope, which presents an abnormally high and abrupt pulse among a series of stable pulses, which also means voltage level or current changes suddenly during a series of stable signals. Reasons for generation of surge include, for example, lightning, breakdown of power system or the like. Although the power station has protection mechanism, some surges may still be transmitted because the protection mechanism has a limit. Furthermore, the protection mechanism may generate a surge resulting in, for example, a switch in a house being turned on or off. Sometimes, the surge may destroy electronic devices such as computers, televisions, stereos or the like since their resistant ability against surge is insufficient.
An inverter itself also generates surges. When the inverter drives a motor, the inverters generates a pulse current, called “inverter surge”, which may damage insulating properties of enameled wire around the motor and interrupt magnetic field of motor, relay, transformer or the like. Generally speaking, surge applies extremely huge loading to the enameled wire. If the enameled wire insulating material does not have sufficient insulating strength or cannot evacuate the loading, an insulating layer is easily broken or destroyed, so a coil wound by the enameled wire may cause short-circuit or transmit unstably, and then the electronic devices cannot function normally or are damaged. Even surge absorber cannot resolve above problems thoroughly. Therefore, insulating material for enameled wire with surge resistance is the key to developing inverters.
For satisfying above demand, some surge-resistant insulating materials were developed. In 1985, General Electric Company (U.S. Pat. No. 4,493,873) published a surge-resistant insulating enamel for forming an insulating layer including metal oxide such as alumina. In 1997, Phelps Dodge Industries, Inc. (U.S. Pat. No. 5,654,095) published a surge-resistant insulating enamel for forming an insulating layer including metallic oxides such as TiO2, Al2O3, Cr2O3, ZnO, or the like. Owing to high dielectric constant of the metallic oxides, the metallic oxides are able to absorb, disperse or evacuate surges, so the insulating layer will not be damaged. For further avoiding damage from surges, multiple layers of coating are applied to an enameled wire. For example, a conductor is coated with a surge-resistant insulating enamel and then is coated with an organic insulating protective coating, so the organic insulating protective coating is able to offset the surge after the surge penetrates the surge-resistant insulating layer. Interface compatibility between the metallic oxides and organic insulating materials is important. If interface compatibility between them is poor, the metallic oxides agglomerate easily to form particles with large sizes. Hence, the metallic oxides are distributed heterogeneously, which lowers dispersion and evacuation of surges.
Inorganic material, such as silica (SiO2), efficiently prevents the enameled wire in a motor from damage by surge generated from corona discharge. Organic insulating material added with inorganic material enhances surge-resistance of the insulating layer. However, inorganic material is not soft enough. If inorganic material is distributed heterogeneously, stress occurs in the enameled wire when the enameled wire is wound into a coil, so electrical and mechanical defaults will damage the enameled wire. Apparently, how to distribute inorganic material homogeneously is a major problem.
In addition to metallic oxides or nano organic silica particles, inorganic material with layer structure can also be added into the insulating layer. JP patent No. 2005-190699, U.S. Pat. Nos. 4,476,192, 5,654,095, 6,906,258 and 2005-0142349 disclose that inorganic material with layer structure improves withstanding pot life of enameled wire for resisting surges. The inorganic material may be modified. As mentioned in the above patents, the inorganic material has a layer structure, wherein the silicate layers and adjacent layers are intercalated by quaternary ammonium salts or quaternary phosphonium salts. Unfortunately, the quaternary ammonium or phosphonium salts may affect the crosslinking density of the insulating polymer, and then results in the brittle insulating layer peeling off from the conductor.
US patent No. 2001/001891 teaches an insulation material which is resistant to high voltage prepared with a polymer resin and inorganic particulate including metal oxides, such as fumed silica. The inorganic particulate including fumed silica are mixed with organic solvent like cresol or phenol. Due to the fumed silica made by a flame hydrolysis process has a small amount of hydroxyl groups on its own surface, the inorganic particulates including fumed silica are distributed heterogeneously over the insulation material and lowering the effectiveness of evacuating surge.
U.S. Pat. No. 6,911,258 teaches an insulation material which has compatibilizing clay with polyethylene oxide and particles including silicate. The insulation material can be modified with compatibilizing clay to increase the dispersity throughout a polymer matrix. However, it is not taught in the patent that the particles comprising/consisting of organic dispersible silica material or silica sol, which has many hydroxyl groups, so it is not sure whether the particles can be distributed evenly in the composition.
To overcome the shortcomings, the present invention provides a surge-resistant and abrasion resistant flexible insulating enamel to mitigate or obviate the aforementioned problems.